Blast-furnace-blow-in charcoal and method for producing same

ABSTRACT

In blast-furnace-blow-in charcoal that is blown in from a tuyere to the interior of a blast furnace main body of a blast furnace facility, the oxygen atom content (on a dry basis) is 10-20 wt % and the average pore size is 10-50 nm.

TECHNICAL FIELD

The present invention relates to blast furnace injection coal and a method of manufacturing the same.

BACKGROUND ART

Blast furnace installations are designed to be capable of manufacturing pig iron from iron ore by charging raw materials such as iron ore, limestone, and coke into the blast furnace main unit through the top and blowing hot air and pulverized coal (PCI coal) as auxiliary fuel through the tuyeres on the lower lateral side.

As such blast furnace injection coal, coals have been proposed which are obtained by adding an oxidant such for example as KMn0₄, H₂O₂, KClO₃, or K₂Cr₂O₄ to pulverized coal in advance to improve the combustion efficiency so that generation of unburned carbon (soot) can be suppressed (see Patent Literature 1 listed below, for example).

Moreover, methods have been proposed which involve, for example, enriching the oxygen in hot air and blowing the air into the blast furnace main unit through the tuyeres to improve the combustibility of the blast furnace injection coal (see Patent Literature 2 listed below, for example).

CITATION LIST Patent Literatures

Patent Literature 1: Japanese Patent Application Publication No. Hei 6-220510

Patent Literature 2: Japanese Patent Application Publication No. 2003-286511 SUMMARY OF INVENTION Technical Problems

However, the blast furnace injection coal described in Patent Literature 1 listed above inevitably requires adding the above-mentioned oxidant to pulverized coal and therefore increases the running cost.

Moreover, the combustibility improving method described in Patent Literature 2 listed above requires operating the blast furnace with a large amount of oxygen constantly added into the hot air and therefore increases the running cost as well.

In view of the above, an object of the present invention is to provide blast furnace injection coal and a method of manufacturing the same which are capable of improving the combustion efficiency at a low cost and suppressing generation of unburned carbon (soot).

Solution to Problems

Blast furnace injection coal according to a first aspect of the invention for solving the above-mentioned problems is blast furnace injection coal to be blown into a blast furnace main unit of a blast furnace installation through a tuyere, characterized in that an oxygen atom content ratio (dry base) is between 10 and 20% by weight, and an average pore size is between 10 and 50 nm.

Blast furnace injection coal according to a second aspect of the invention is the first aspect of the invention, characterized in that a pore volume is between 0.05 and 0.5 cm³/g.

Blast furnace injection coal according to a third aspect of the invention is the first or second aspect of the invention, characterized in that a specific surface area is between 1 and 100 m²/g.

A method of manufacturing blast furnace injection coal according to a fourth aspect of the invention for solving the above-mentioned problems is a method of manufacturing the blast furnace injection coal according to any one of the first to third aspect of the invention, characterized in that the method comprises: a drying step of heating subbituminous coal or brown coal to remove moisture; and a pyrolysis step of performing pyrolysis at a temperature between 460 and 590° C. on the coal dried in the drying step.

The method of manufacturing blast furnace injection coal according to a fifth aspect of the invention is the fourth aspect of the invention, characterized in that the method further comprises: a cooling step of cooling the coal subjected to the pyrolysis in the pyrolysis step to a temperature between 50 and 150° C.; and a partially oxidizing step of partially oxidizing the coal cooled in the cooling step by exposing the coal in an oxygen-containing atmosphere at a temperature between 50 and 150° C. to let the coal chemically adsorb oxygen.

Advantageous Effects of Invention

According to the blast furnace injection coals according to the present invention, the average pore size is 10 to 50 nm, that is, tar producing groups such as oxygen-containing functional groups (such as carboxyl groups, aldehyde groups, ester groups, and hydroxyl groups) desorb and greatly decrease, while the oxygen atom content ratio (dry base) is 10 to 20% by weight, that is, decomposition (decrease) of the main skeletons (combustion components mainly containing C, H, and O) is greatly suppressed. Hence, when such blast furnace injection coal is blown into the blast furnace main unit through the tuyere together with hot air, the blast furnace injection coal can be completely combusted with almost no unburned carbon (soot) generated because many oxygen atoms are contained in the main skeletons and also because the large-sized pores allow the oxygen in the hot air to be easily spread to the inside and also significantly suppresses the production of tar. Accordingly, it is possible to improve the combustion efficiency at a low cost and suppress generation of unburned carbon (soot).

According to the method of manufacturing the blast furnace injection coal according to the present invention, the blast furnace injection coals described above can be manufactured at a low cost.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flowchart showing the procedure of a first embodiment of a method of manufacturing blast furnace injection coal according to the present invention.

FIG. 2 is a flowchart showing the procedure of a second embodiment of the method of manufacturing blast furnace injection coal according to the present invention.

FIG. 3 is a graph showing the relation between the temperature of subbituminous coal and the ratio of content of each of its oxygen-containing functional groups based on an infrared absorption spectrum of the subbituminous coal measured with its temperature is raised under a nitrogen-containing atmosphere.

FIG. 4 is a graph showing the relation between the ratios of unburned carbon collected after present invention coal, dried coal, and conventional coal are combusted, and the concentrations of residual oxygen (excess oxygen concentrations) in combustion exhaust gases after the combustion.

FIG. 5 is a graph showing the relation between the excess oxygen ratio and the combustion temperature of complete combustion of each of the present invention and the conventional coal.

DESCRIPTION OF EMBODIMENTS

Embodiments of a blast furnace injection coal and a method of manufacturing the same according to the present invention will be described with reference to the drawings. However, the present invention is not limited only to the embodiments to be described below with reference to the drawings.

First Embodiment

A first embodiment of the blast furnace injection coal and the method of manufacturing the same according to the present invention will be described with reference to FIG. 1.

The blast furnace injection coal according to this embodiment has an oxygen atom content ratio (dry base) of 10 to 18% by weight and an average pore size of 10 to 50 nm (nanometer) (preferably 20 to 50 nm (nanometer)).

As shown in FIG. 1, the blast furnace injection coal according to this embodiment as mentioned above can be easily manufactured by: drying low-rank coal (oxygen atom content ratio (dry base): over 18% by weight, average pore size: 3 to 4 nm) 11 such as subbituminous coal or brown coal by heating it (at 110 to 200° C.×0.5 to 1 hour) in a low oxygen atmosphere (oxygen concentration: 5% by volume or lower) to remove moisture (drying step S11); performing pyrolysis on the resultant coal by heating it (at 460 to 590° C. (preferably 500 to 550° C.)×0.5 to 1 hour) in a low oxygen atmosphere (oxygen concentration: 2% by volume or lower) to remove produced water, carbon dioxide, tar, and the like as pyrolysis gas and pyrolysis oil (pyrolysis step S12); cooling the resultant coal (to 50° C. or below) in a low oxygen atmosphere (oxygen concentration: 2% by volume or lower) (cooling step S13); and pulverizing the resultant coal (to a particle size: 77 μm or smaller (80% pass)) (pulverizing step S14).

In blast furnace injection coal 12 manufactured by the manufacturing method according to this embodiment as described above, the average pore size is 10 to 50 nm, that is, tar producing groups such as oxygen-containing functional groups (such as carboxyl groups, aldehyde groups, ester groups, and hydroxyl groups) desorb and greatly decrease, while the oxygen atom content ratio (dry base) is 10 to 18% by weight, that is, decomposition (decrease) of the main skeletons (combustion components mainly containing C, H, and O) is greatly suppressed. Hence, when the blast furnace injection coal 12 is blown into a blast furnace main unit through each tuyere together with hot air, the blast furnace injection coal 12 can be completely combusted with almost no unburned carbon (soot) generated because many oxygen atoms are contained in the main skeletons and also because the large-sized pores allow the oxygen in the hot air to be easily spread to the inside and also significantly suppresses the production of tar.

Hence, the blast furnace injection coal 12 according to this embodiment can improve the combustion efficiency and suppress generation of unburned carbon (soot) without adding an oxidant such as KMn0₄, H₂O₂, KClO₃, or K₂Cr₂O₄ or enriching the oxygen in the hot air.

Thus, according to this embodiment, it is possible to improve the combustion efficiency at a low cost and suppress generation of unburned carbon (soot).

Note that the average pore size of the blast furnace injection coal 12 according to this embodiment needs to be 10 to 50 nm (preferably 20 to 50 nm). This is because if the average pore size is smaller than 10 nm, the spreadability of the oxygen in the hot air to the inside will be deteriorated and the combustibility will be accordingly deteriorated, whereas if the average pore size is larger than 50 nm, the blast furnace injection coal 12 will easily crack into smaller sizes due to heat shock and the like, and will therefore crack into smaller sizes when blown into the blast furnace main unit, which leads to a situation where the blast furnace injection coal 12 passes through the inside of the blast furnace main unit with a gas stream and is discharged without combustion.

Moreover, the oxygen atom content ratio (dry base) needs to be not smaller than 10% by weight as well. This is because it will be difficult to achieve complete combustion without adding an oxidant or enriching the oxygen in the hot air if the oxygen atom content ratio (dry base) is smaller than 10% by weight.

Furthermore, the pore volume is preferably 0.05 to 0.5 cm³/g and particularly preferably 0.1 to 0.2 cm³/g. This is because the surface area of contact (surface area of reaction) with the oxygen in the hot air will be small and the combustibility will possibly be deteriorated if the pore volume is smaller than 0.05 cm³/g, whereas large amounts of components will volatilize and the blast furnace injection coal 12 will be so porous that the combustion components may be excessively reduced if the pore volume is larger than 0.5 cm³/g.

In addition, the specific surface area is preferably 1 to 100 m²/g and particularly preferably 5 to 20 m²/g. This is because the surface area of contact (surface area of reaction) with the oxygen in the hot air will be small and the combustibility will possibly be deteriorated if the specific surface area is smaller than 1 m²/g, whereas large amounts of components will volatilize and the blast furnace injection coal 12 will be so porous that the combustion components may be excessively reduced if the specific surface area is larger than 100 m²/g.

On the other hand, in the method of manufacturing the blast furnace injection coal according to this embodiment, the temperature of the pyrolysis in the pyrolysis step S12 needs to be 460 to 590° C. (preferably 500 to 550° C.). This is because, the tar producing groups such as oxygen-containing functional groups will fail to be desorbed sufficiently from the low-rank coal 11 and it will be extremely difficult to obtain an average pore size of 10 to 50 nm if the temperature is lower than 460° C., whereas the decomposition of the main skeletons (combustion components mainly containing C, H, and O) of the low-rank coal 11 will start to be remarkable, and large amounts of component will volatilize, which in turn excessively reduces the combustion components, if the temperature is higher than 590° C.

Second Embodiment

A second embodiment of the blast furnace injection coal and the method of manufacturing the same according to the present invention will be described with reference to FIG. 2. Note that for portions similar to those in the foregoing embodiment, reference signs similar to the reference signs used in the description of the foregoing embodiment will be used, and their description overlapping the description in the foregoing embodiment will be omitted.

The blast furnace injection coal according to this embodiment has an oxygen atom content ratio (dry base) of 12 to 20% by weight and an average pore size of 10 to 50 nm (preferably 20 to 50 nm).

As shown in FIG. 2, the blast furnace injection coal according to this embodiment as mentioned above can be easily manufactured by: drying the low-rank coal (oxygen atom content ratio (dry base): over 18% by weight) 11 in a similar way to the foregoing embodiment (drying step S11); performing pyrolysis on the resultant coal in a similar way to the foregoing embodiment (pyrolysis step S12); cooling the resultant coal (to 50 to 150° C.) in a low oxygen atmosphere (oxygen concentration: 2% by volume or lower) (cooling step S23); partially oxidizing the resultant coal by exposing it to an oxygen-containing atmosphere (oxygen concentration: 5 to 21% by volume) (at 50 to 150° C.×0.5 to 10 hours) to let the coal chemically adsorb oxygen (partially oxidizing step S25); and pulverizing the resultant coal in a similar way to the foregoing embodiment (pulverizing step S14).

In sum, in this embodiment, the coal subjected to the pyrolysis in the pyrolysis step S12 is cooled to 50 to 150° C., and the coal is then partially oxidized by letting the coal chemically adsorb oxygen in the partially oxidizing step S25, to thereby obtain blast furnace injection coal 22 having an oxygen atom content ratio (dry base) of 12 to 20% by weight.

In the blast furnace injection coal 22 manufactured by the manufacturing method according to this embodiment as mentioned above, like the foregoing embodiment, the average pore size is 10 to 50 nm, that is, tar producing groups such as oxygen-containing functional groups (such as carboxyl groups, aldehyde groups, ester groups, and hydroxyl groups) desorb and greatly decrease, while the oxygen atom content ratio (dry base) is 12 to 20% by weight, that is, decomposition (decrease) of the main skeletons (combustion components mainly containing C, H, and O) is greatly suppressed, and more oxygen atoms have chemically adsorbed. Hence, when the blast furnace injection coal 22 is blown into the blast furnace main unit through the tuyere together with hot air, the blast furnace injection coal 22 can be completely combusted with less unburned carbon (soot) generated than in the foregoing embodiment because the main skeletons contains more oxygen atoms than in the foregoing embodiment and also because the large-sized pores allow the oxygen in the hot air to be easily spread to the inside and also significantly suppresses the production of tar like the foregoing embodiment.

Hence, the blast furnace injection coal 22 according to this embodiment can improve the combustion efficiency to a greater extent and suppress generation of unburned carbon (soot) more reliably than in the foregoing embodiment without adding an oxidant such as KMn0₄, H₂O₂, KClO₃, or K₂Cr₂O₄ or enriching the oxygen in the hot air.

Thus, according to this embodiment, it is possible to further improve the combustion efficiency at a low cost and suppress generation of unburned carbon (soot) more reliably than in the foregoing embodiment.

Note that the oxygen atom content ratio (dry base) of the blast furnace injection coal 22 according to this embodiment needs to be 20% by weight or lower. This is because the oxygen content will be excessively large and the amount of heat generation will be excessively reduced if the oxygen atom content ratio (dry base) is smaller than 20% by weight.

On the other hand, in the method of manufacturing the blast furnace injection coal according to this embodiment, the temperature of the process in the partially oxidizing step S25 is preferably 50 to 150° C. This is because it will be difficult to advance the partial oxidation process even in an air (oxygen concentration: 21% by volume) atmosphere if the temperature is lower than 50° C., whereas large amounts of carbon monoxide and carbon dioxide will possibly be generated by the combustion reaction even in an atmosphere where the oxygen concentration is about 5% by volume if the temperature is higher than 150° C.

EXAMPLES

Examples carried out for the purpose of confirming the advantageous effects of the blast furnace injection coal and the method of manufacturing the same according to the present invention will be described below. However, the present invention is not limited only to the examples to be described below based on various kinds of data.

<No. 1: Composition Analysis>

A composition analysis (ultimate analysis) was performed on the blast furnace injection coal 12 obtained by the manufacturing method according to the first embodiment described above (present invention coal). Moreover, for comparison, a composition analysis was performed also on conventional blast furnace injection coal (PCI coal: conventional coal), and on coal obtained by omitting the pyrolysis step S12 in the first embodiment (dried coal). Table 1 given below shows the results. Note that the values are all on the dry base.

TABLE 1 Present Invention Conventional Dried Coal Coal Coal C (wt. %) 73.8 84.5 71.0 H (wt. %) 3.2 3.8 3.6 O (wt. %) 14.4 2.9 18.5 N (wt. %) 1.1 1.7 1.0 S (wt. %) 0.3 0.5 0.5 Calorific Value 6700 8020 6300 (kcal/kg)

As can be seen from Table 1 given above, the oxygen (O) ratio of the present invention coal is smaller than that of the dried coal and significantly larger than that of the conventional coal, while the carbon (C) ratio is larger than that of the dried coal and smaller than that of the conventional coal. Thus, the calorific value of the present invention coal is larger than that of the dried coal and smaller than that of the conventional coal.

<No. 2: Surface States>

Surface states (average pore size, pore volume, specific surface area) of the above present invention coal were measured. Moreover, for comparison, the surface states of the above conventional coal and dried coal were measured as well. Table 2 given below shows the results.

TABLE 2 Present Invention Conventional Dried Coal Coal Coal Average Pore Size (nm) 20 1.5 3.5 Pore Volume (cm³/g) 0.13 0.08 0.14 Specific Surface Area 10.4 0.23 15 (m²/g)

As can be seen from Table 2 given above, the average pore size of the present invention coal is significantly larger than those of the conventional coal and the dried coal.

<No. 3: Amounts of Oxygen-Containing Functional Groups>

An infrared absorption spectrum of subbituminous coal (PRB coal from the United States) was measured with its temperature raised (10° C./min) under a nitrogen-containing atmosphere to find the ratio of the content of each of oxygen-containing functional groups (hydroxyl groups (OH), carboxyl groups (COOH), aldehyde groups (COH), ester groups (COO)) at given temperatures. FIG. 3 shows the result. Note that the horizontal axis represents the temperature, and the vertical axis represents the ratio of the peak area of each oxygen-containing functional group to the whole peak area of the oxygen-containing functional groups at 110° C.

As can be seen from FIG. 3, the above oxygen-containing functional groups, i.e. the tar producing groups are confirmed to mostly disappear at 460° C. and completely disappear at 500° C.

<No. 5: Combustibility>

The relation between the ratio of residual unburned carbon resulting from combustion of the above present invention coal with air at 1500° C., and the flow rate of the fed air was found. Moreover, for comparison, the relation was found also for the above conventional coal and dried coal. FIG. 4 shows the results. Note that in FIG. 4, the horizontal axis represents the concentration of residual oxygen in combustion exhaust gas after the combustion of the coal, i.e. excess oxygen concentration, and the vertical axis represents the ratio of unburned carbon collected after the combustion of the coal.

As can be seen from FIG. 4, in the cases of the conventional coal and the dried coal, the amount of unburned carbon gradually increases as the excess oxygen concentration decreases. In contrast, in the case of the present invention coal, the amount of unburned carbon does not increase even when the excess oxygen concentration decreases. Thus, the present invention coal is confirmed to be capable of substantially complete combustion.

<No. 5: Combustion Temperature>

The relation between the excess oxygen ratio and the combustion temperature of 100% complete combustion of the above present invention coal under the conditions given below was found. Moreover, for comparison, the relation was found also for the above conventional coal. FIG. 5 shows the results. Note that an excess oxygen ratio Os is a value defined by the formula (1) given below.

Combustion Formulas

C+O₂→CO₂

H₂+½O₂→H₂O

Combustion Conditions

-   -   Temperature of fed air: 1200° C.     -   Concentration of oxygen in air: 21 vol.%     -   Temperature of fed coal: 25° C.     -   Moisture Content: 2%

Excess Oxygen Ratio

Os=(Oa+Oc/2)/(Cc+Hc/4)  (1)

where Oa is the molar flow rate of the oxygen gas (molecules) in the fed air, Oc is the molar flow rate of the oxygen atoms in the fed coal, Cc is the molar flow rate of the carbon atoms in the fed coal, and Hc is the molar flow rate of the hydrogen atoms in the fed coal.

As can be seen from FIG. 5, although the calorific value of the present invention coal is smaller than that of the conventional coal, the combustion temperature is confirmed to be higher than that of the conventional coal in a case where the excess oxygen ratio is the same as that of the conventional coal. This is because the present invention coal has a larger oxygen content ratio than the conventional coal does, and therefore only requires a smaller amount of fed air than the conventional coal does on condition that the excess oxygen ratio is the same as that of the conventional coal.

INDUSTRIAL APPLICABILITY

The blast furnace injection coals and the methods of manufacturing the same according to the present invention can be utilized significantly beneficially in the coal industry, steel industry, and the like.

REFERENCE SIGNS LIST

-   11 LOW-RANK COAL (SUBBITUMINOUS COAL OR BROWN COAL) -   12, 22 BLAST FURNACE INJECTION COAL -   S11 DRYING STEP -   S12 PYROLYSIS STEP -   S13, S23 COOLING STEP -   S14 PULVERIZING STEP -   S25 PARTIALLY OXIDIZING STEP 

1. Blast furnace injection coal to be blown into a blast furnace main unit of a blast furnace installation through a tuyere, wherein an oxygen atom content ratio (dry base) is between 10 and 20% by weight, and an average pore size is between 10 and 50 nm.
 2. The blast furnace injection coal according to claim 1, wherein a pore volume is between 0.05 and 0.5 cm³/g.
 3. The blast furnace injection coal according to claim 1, wherein a specific surface area is between 1 and 100 m²/g.
 4. A method of manufacturing the blast furnace injection coal according to claim 1, wherein the method comprises: a drying step of heating subbituminous coal or brown coal to remove moisture; and a pyrolysis step of performing pyrolysis at a temperature between 460 and 590° C. on the coal dried in the drying step.
 5. The method of manufacturing the blast furnace injection coal according to claim 4, wherein the method further comprises: a cooling step of cooling the coal subjected to the pyrolysis in the pyrolysis step to a temperature between 50 and 150° C.; and a partially oxidizing step of partially oxidizing the coal cooled in the cooling step by exposing the coal in an oxygen-containing atmosphere at a temperature between 50 and 150° C. to let the coal chemically adsorb oxygen. 